The present invention relates to a glass-ceramic plate intended in particular to cover or receive heating elements, in particular intended to serve as a cooking plate, the heating elements associated with this plate being in particular of induction heating hobs.
Sales of glass-ceramic cooking plates have been constantly increasing for several years. This success is explained in particular by the attractive appearance of these plates and by their ease of cleaning.
It should be recalled that a glass-ceramic originates from a glass, called a precursor glass, of which the specific chemical composition makes it possible to bring about controlled crystallisation by suitable heat treatments called ceramization. This specific partly crystallized structure gives the glass-ceramic unique properties.
Various types of glass-ceramic plates currently exist, each variant being the result of sizeable studies and many tests, given that it is very difficult to make modifications to these plates and/or to the method for obtaining them without risking an unfavorable effect on the desired properties: in order to be usable as a cooking plate, a glass-ceramic plate must in particular have a transmission in wavelengths of the visible region that is at the same time sufficiently low in order to mask at least partly the subjacent heating elements at rest and sufficiently high, so that, with the aim of safety, the user can visually detect the heating elements in the operating state. Generally, it must also have a high transmission at wavelengths in the infrared region.
The first plates developed have therefore been plates with a dark color, in particular black. More recently, other plates have been developed with a lighter appearance (in particular white) and having for example a blur or haze of at least 50% (as described in patent FR2766816), the previously mentioned criteria (such as the detection of heating elements in the operating state without dazzle from said elements or without an unattractive appearance of these) sometimes being taken into account to the detriment of other aspects (such as the clear appearance of any display positioned under the plate).